Need help urgent with error!!

[Tiglet]

I got this code (a snippet):

    class PrintMenu

    {

        public int Hoofdmenu()

        {

            try{

                Console.Clear();

                int Keuze = 0;

                Console.WriteLine("**** Welkom bij het DBA project van Vandersteegen Jan ****");

                Console.WriteLine("----------------------------------------------------------\n\n");

                Console.WriteLine("Kies wat u wilt doen: \n");

                Console.WriteLine("  |***********************************************************************|");

                Console.WriteLine("  | 1: Inlezen van CSV bestand met nieuwe gebruikers om aan te maken.     |");

                Console.WriteLine("  | 2: Exporteren van bestaande gebruikers naar een CSV bestand           |");

                Console.WriteLine("  | 3: Verwijderen van bestaande gebruikers op basis van een CSV bestand  |");

                Console.WriteLine("  | 4: Afsluiten van het programma                                        |");

                Console.WriteLine("  |***********************************************************************| \n\n");

                Console.Write("U keuze: ");

                Keuze = int.Parse(Console.ReadLine());

				

                return Keuze;

           }

            catch (Exception ex)

           {
      ......

at the part where it says: Keuze = int.Parse(Console.ReadLine());
I get an error. It looks like it keeps skipping the readline part and just tries to convert nothing to a integer.
I tried making a seperate string variable for my input and then converting it to an int but that just gives me the same error... just like its skipping the readline like I said, and doesn't wait for my input :s

Any help would be very appreciated.

to be exact it's this error:

System.ArgumentNullException: Argument cannot be null.
Parameter name: s
at System.Int32.Parse (System.String s) [0x00000]
at VandersteegenJan_DBAProject_2010.PrintMenu.Hoofdme nu () [0x0006b] in /home/jean/Desktop/VandersteegenJan-DBAProject-2010/VandersteegenJan-DBAProject-2010/Program.cs:138

this all works in windows visual studio but not in monodeveloper 2.2 on linux